There has been known a so-called Lundell-type generator as a generator used in, for example, an alternator of an automobile (Patent Literature 1 and 2).
An example of the Lundell-type generator is shown in FIG. 12 and FIG. 13. The shown Lundell-type generator includes: a substantially hollow cylindrical stator 110, a rotary shaft 120 disposed coaxially with the stator 110 on the inner side of the stator 110, first and second rotor iron-cores 121 and 122, a rotor coil (an excitation coil) 124, a front cover 130, and a rear cover 140 which is a hollow cylindrical frame body.
The stator 110 includes magnetic cores 112 and stator coils 114. The magnetic cores 112 are disposed to extend inward from a plurality of positions on the inner surface of the casing 130. The stator coils 114 are wound around the circumference of the magnetic cores 112, respectively. The magnetic cores 112 are usually formed of a large number of non-directional electromagnetic steel plates (or silicon steel plates) mutually and axially stacked. Each of the electromagnetic steel plates has a thickness of 0.5 mm or less.
The rotary shaft 120 is supported, by a bearing fixed to the front cover 130 and the rear cover 140, so as to be coaxial with the stator 110 and relatively rotatable to the stator 110. Each of the rotor iron-cores 121 and 122 is firmly attached onto the outer circumferential surface of the rotary shaft 120 by shrinkage fitting and includes a doughnut-plate-shaped base 126 and a plurality of claw-shaped magnetic poles (called claw poles) 128 projecting from the base 126 along the axial direction. The rotor iron-cores 121 and 122 are disposed so as to orient the magnetic poles 128 thereof in opposite directions to each other and so as to circumferentially arrange the magnetic poles 128 thereof alternately, that is, so as to mesh the magnetic poles 128 thereof with each other in a comb teeth-shape. The rotor coil 124 is disposed between the rotary shaft 120 and the craw-shaped magnetic poles 128 to generate magnetic fluxes in the craw-shaped magnetic poles 128 of the rotor iron-cores 121 and 122 when energized.
The rotor coil 124 is connected to an external power supply 150, through a hollow hole and a side groove provided in the rotary shaft 120 and through a slip ring brush 129 provided at an end portion of the rotary shaft 120 as shown in FIG. 14, to receive supply of an excitation current from the power supply 150. The rotor coil 124, thereby, excites the craw-shaped magnetic poles 128 of both the rotor iron-cores 121 and 122 disposed in the comb teeth-shape each other to an N pole and an S pole alternately. The craw-shaped magnetic poles 128 thus energized rotate to change the N pole and the S pole alternately, thereby vary a line of magnetic flux piercing through the inner side of the stator coils 114 changes in an alternating current manner; this generates a potential difference in a conductor forming the stator coil 114 to supply an electric current to a load connected to the outside. This is the principle of the Lundell-type alternating-current generator.
The comb teeth-like rotor magnetic poles 128 of the Lundell-type generator are often used mainly in a generator for an engine automobile, since the field magnetomotive force is adjustable by the excitation of the rotor coil 124 disposed inside the comb teeth-like rotor magnetic poles 128, which allows magnetic flux adjustment in accordance with rotational speed and a rotational output to be easily performed. In such a small generator, the comb teeth-like (craw-shaped) magnetic poles (claw poles) 128 are usually formed integrally with the base 126 as a single member molded from a magnetic metal lump by forging (or by cutting, in the case of special and few production). In short, the rotor iron-cores 121 and 122 are usually formed of a bulk magnetic iron lump (see Patent Literature 2).
The conventional Lundell-type generator including the lump-like rotor iron-cores 121 and 122, involving a large energy loss due to generation of an eddy current depending on a form of use of the Lundell-type generator, has a problem that the range of uses thereof is extremely limited. For example, if the conventional Lundell-type generator shown in FIG. 12 and FIG. 13 was applied to fields of products where a high output and high efficiency are required such as a large generator, a hybrid car, and an electric vehicle, there could be flowed considerably large alternating current containing harmonics in the stator coils 114; this would permit diamagnetic-field-flux-lines generated by the stator coils 114 to intrude into the lump-like magnetic poles 128 of the rotor iron-cores 121 and 122 to produce eddy current in the surfaces and under the surface skins of the magnetic poles 128, thereby causing conspicuous energy loss.
Besides, in recent years, concerning a small vehicle as well, there is an increasing demand for an ecological vehicle with small size and weight and with high fuel efficiency, so called μ-HV, and it is examined, for the reduction in weight, to make temporary use of an alternator exclusive for power generation also as a starter motor and a regenerative brake; however, also in the case of applying the Lundell-type generator shown in FIG. 12 and FIG. 13 to the alternator, flowing an alternating current or a pulse current into the stator coil 114 from the outside would permit an alternating-current flux lines to intrude into the magnetic poles 128 of the rotor iron-cores 121 and 122. The magnetic lump, such as commercial pure iron, which configures the magnetic poles 128 has not only high magnetic permeability but also high electric conductivity, permitting eddy current to be generated inside the magnetic poles 128 to thereby cause a large (heat) loss and to markedly deteriorate efficiency.
As means for suppressing the generation of the eddy current, known is forming rotor magnetic poles of a stacked body formed by a large number of electromagnetic steel plates; however, it is difficult to directly apply the conventional stacked structure formed by the electromagnetic steel plates and the like to the rotor magnetic poles, since the plurality of rotor magnetic poles forming the Lundell-type generator are integrally joined with the base of the common rotor iron-core to have a complicated shape (so-called claw poles) projecting in a comb teeth shape from the base along the axial direction. Regarding this point, Patent Literature 1 discloses dividing a rotor magnetic pole into a plurality of components and forming the respective components of stacked structures of plane electromagnetic steel plates; however, such a structure is extremely complicated and includes a large number of components, for example, respective bolts for fastening the respective magnetic poles, and assembly thereof is also difficult. Moreover, it is impossible to avoid deterioration in effective magnetic resistance involved by air gaps caused between respective joining surfaces of the electromagnetic steel plates stacked mutually or use of a nonmagnetic insertion object such as a fastening tool. The structure is, thus, poor in practicality.